Method for the separation and recovery of krypton and xenon from gaseous mixtures containing them



May 12, 1936. J. SCHLITT' 2,040,107-

METHOD FOR THE SEPARATION AND RECOVERY OF KRYPTON AND XENON FROM GASEOUS MIXTURES CONTAINING THEM I Filed April 9, 1935 X 5 M: am 5 v w "4 E b U Q N E E b Q '3 a 35 g, F

INVENTOR Jose M Z BY ATTQRNEY5 80 condensed-portion.

Patented May 12, 1936 UNITED- STATES METHOD FOR THE SEPARATION AND RE- COVERY OF; KRYPTON AND XENON FROM GASEOUS MIXTURES CONTAINING THEM Joseph L. Schiitt, Darien, Comm, assignor to Air Reduction Company, Incorporated, New

York, N. Y,, a corporationof New York Application April 9. 1935; ,Serial. No. 15,403

r z Claims. (01. esp-115,5)

The invention relates to the economical separation of the gases krypton and xenon from mixtures containing them such as atmospheric air or atmospheric residual gases from which the 5 components oxygen and nitrogen have been more or less completely removed .previously..

The present method is not intended to recove either of the two atmospheric gases. oxygen or nitrogen in commercial purity from the atmospheric air or other mixture treated, but is directed to an economical method of recovering the elementskrypton and xenon in a stateof purity suitable for further purification by chemical or adsorption methods. a

The method is characterized by the important feature that only a relatively small fraction of the total air treated is liquefied. The major portion of the gaseous mixture passes through the cycle unliquefied and this feature makes possible the operation of the method at relatively low cost. The krypton and xenon are caused to concentrate in that small portionmf 1 the original mixture which is condensed and the loss ofthese gases in the major uneondensed portion is pracfli tically nil. t

a The unliquefied gaseous portion is composed of both oxygen and nitrogen, therel'ative percentage of. nitrogenand oxygen being somewhat increased as the result of the liquefaction of the Nowhere in the method, however, is oxygen produced in a puritysuitable for industrial applications existing today:= i a The liquefied portion, that is the krypton- 85 xenon concentrate, is further treated in order to obtain the krypton and xenon with a purity suitable for further purification treatment by well known methods. This is accomplished by means of re-evaporation of thekrypton-x'enon 40 liquid concentrateiollowedbwamoderate compression and then by means of selective liquefaction and rectification, mostof the-impurities oxygen and nitrogen are separated from the krypton-xenon as hereinafter described.

The details of the method may be more readily understood by reference to the accompanying 'diagrammaticdr'awing, which illustrates an apparatus suitable for the practice of the invention. Details of apparatus well known in the art 50 are omitted for the purpose of clarity.

The air. or other gaseous mixture containing krypton and xenon is delivered by a pipe 5 to a compressor or blower 6 and after traversing pipe 'l enters compartment 8 of an exchanger 9 where- 55 in it is cooled by thermal contact with outgoing products. The gaseous mixture then passes through apipe It] to an exchanger ll wherein it is still further cooled. to a temperature in the neighborhood of its dew point. A pipe .ll delivers the gaseous mixture to thes'elective condenser, in which itpasses upwardly and is partiallyliquefied by thermal contact with the cold fluid traversing coil I4. at the .top level of condenser l3. This coil condenses a portion of the rising vapors which collect in a pool at the bottom of condenser I3.

wThe liquid leaves pool l5 by means o! pipe l6 and passes through a pressure reducing valve I! wherein its pressure (and temperature) is lowered sufliciently for use as condensing liquid in coil ll. r

The uncondensed vapors leaving condenser 13 through pipe l8 traverseexchanger H and by means of pipe I 9 enter the turbo-expander in which the temperature is again reduced substantially by reason of its expansion with external work inturbo-expander 20. v From the latter the working fluid leaves through pipe 2| and the major portion passes outward through exchangersgll and 9 by means of pipes 22, 23, 24 and 25.

.A portion of the exhaust from turbo-expander 20 isdiverted through pipe 26 tothe exchanger 21. for reasons hereinafter described. leaving exchanger 21 by means of pipe 28 itjoins that portion of the exhaust passing through exchanger Hinpipe24.

The pressure necessary to beproduced in compressor 6 is determined primarily by the necessity of the vapors rising in condenser l3to be partiallycondensed by means of the lower pressure liquidcirculating through coil 14. Since the quantity of fluid liquefied by coil I4 isonly a small portion of the total, the composition of the vapor rising to the top of condenser l3 and. leaving by means of pipe 18 is not greatly different from that of atmospheric -airasiar'as oxygen and nitrogen are concerriedandthus the pressure necessary to accomplish 'the condensation in condenser I3 is relatively small, "for ex-' ample, from 1 to 2 atmospheres gauge, assuming i3 is that the pressure in condenser-rectifier 1 atmosphere.

The turbo-expander 20 aflords the refrigeration necessary in the system in order to overcome external heat leakage into the apparatus. The reirigerative efiect produced by expander '20 may be increased either by an increase of pressure in the fluid leaving compressor 8 or, as an alternative, by reduclngthe pressure in the exhaust of expander 20 by means of a vacuum pump up to that of atmospheric by thermal contact with the incoming mixture. It is then compressed in turbo-compressor a to a pressure suitable for its subsequent liquefaction as hereinafter de-- scribed.

After compression, the krypton-xenon concentrate enters, by pipe 3 I, an exchanger 32 traversing compartment 33 and thence by means of pipe 34 it enters the exchanger 21 traversing the compartment 35 wherein its temperature is reduced to the vicinity of the dew point. Thence by means of a pipe 36, it enters the bottom of the rectification-condensation column 31 and passes upward through the tubular system 32 wherein it is selectively liquefied. The liquefied portion collects in pool39 while the unliquefied portion enters the inner tubularsystem 40 and is therein completely liquefied, to provide a second liquefied portion.

The first liquefied portion leaves the pool 39 by a pipe 4| and passes throughthe pressure reducing valve 42 wherein its pressure is lowered to that prevailing in the interior of rectifier column 3'! which it enters at an intermediate level by means of a pipe 43. The second liquefied portion condensed in the tubes 40 passes through pipe 44 and pressure reducing valve 45 and thence by means of a pipe 46 as top refiux liquid into the top level of the rectifier column 31.

Since the vapor entering tubular system 38 is an uncondensed residue of the mixture entering through the pipe 36, it will be practically free from krypton and xenon and after its condensation in tubes 38, it will be able to liquefy out the krypton and xenon from a large volume of vapor containing these elements. This volume of vapor may be many times that of the vapor ascending 'in rectifier 31 from the bottom. For this reason, it is very advantageous to admit to an intermediate level of rectifier 31 a substantial'quantity of unseparated air which is delivered to the system by the turbo-blower 41. The pressure necessary to be delivered by blower 41, is only that required to cover pipe friction to and from exchanger 32 and rectifier 31.

The feature just described is responsible for an important economy in the system; and together with the advantages and economies already pointed out, renders this method by far the most ellicient for the recovery of krypton and xenon from mixtures containing them.

The rectifier column 31 separates the incoming mixtures entering it through pipe 36 into two products, (1) the top gaseous product consisting only of oxygen and nitrogen plus small percentages of neon, helium and argon and (2) the bottom product which constitutes the final krypton-xenon concentrate. Product (1) leaves the top of rectifier column 31 by means of pipe 48 and passes outward through compartmentv 49 of exchanger 32. Product (2) constituting the krypton-xenon concentrate leaves rectifier column 31 either in the vapor or liquid state by means of pipe and valves 50 and 5|, and traverses exchanger 32 by means of pipe 52 and compartment 53.

In the operation of the method, the pressure in coil l4 may be lowered, if desirable, to a subatmospheric pressure by means of turbo-compressor 30a as already described. In this case, the pressure necessary in condenser-rectifier I3, i. e., the pressure delivered by compressor 6, may

, be lowered correspondingly. In either case, however, the pressure differential between condenserrectifier l3 and coil I 4 is much smaller than for any air separation process because the vapor to be condensed by coil l4 contains substantial quantities of oxygen and thus will condense more easily than pure nitrogen, while the liquid passing through coil M which produces this-condensation contains substantial quantities of nitrogen (around 50%) and thus is much colder at any given pressure than would be pure oxygen at the same pressure. An analogous statement'may be made in regard to the liquefaction and evaporation in the tubular systems'38 and 40.

The present method, it is now evident, has as its most important feature the employment of very low pressures relative to the pressures commonly used in the separation of air into its constituent gases. In fact, every pressure produced in the method may be easily attained by means of turbo-compressors. The economy of the method is also increased by reason of the fact that only a very small fraction of the mixture treated is necessary to be liquefied.

Various changes may be made in the procedure and in the details of the apparatus employed without departing from the invention or sacrificing any of the advantages thereof.

I claim:

1. The method of separating and recovering krypton and xenon from air which comprises liquefying selectively a portion of the air to be treated to secure a liquid enriched in krypton and xenon, evaporating the liquid to effect by heat exchange the selective liquefaction of the incoming air, recompressing and cooling the vapor from the enriched liquid, subjecting the vapor to further selective liquefaction, rectifying the liquid products with the addition of a relatively large volume of unseparated air, and withdrawing the liquid product of the rectification consisting essentially of krypton and xenon.

2. The method of separating and recovering krypton and xenon from airwhich comprises liquefying selectively a portion of the air to be treated to secure a liquid enriched in krypton and xenon, evaporating the liquid at subatmospheric pressure to effect by heat exchange the selective liquefaction of the incoming air, recompressing and cooling the vapor from the enriched liquid, subjecting the vapor to further selective liquev faction, rectifying the liquid products with the addition of a relatively large volume of unseparated air, and withdrawing the liquid product of the rectification consisting essentially of krypton and xenon.

' JOSEPH L. SCHLII'I. 

